Frequently asked questions

When a transformer is equipped with DryKeep® how long before the moisture level will start to reduce?

DryKeep® starts reducing the moisture level immediately.  How long it takes to dry out the insulation depends upon the size of the transformer and how wet it was before the DryKeep® was installed.  For example, a 20 mva transformer probably would dry out in 10 to 12 months. Once you dry it down to a safe level (~1.3%), you would only need to change the cylinders every 5 or 6years. Larger transformers could take up to 2 years to dry down to a safe level.

How do we know which one of the cylinders is saturated?

All 3 cylinders on the DryKeep® RT-9 become saturated at the same time and are replaced as a group.

Cylinder replacement instructions can also be found here.

How and when do we check for cylinder(s) saturation?

DryKeep® can be purchased with an optional moisture measurement instrument package, installed in a cabinet, which measures both the oil temperature and the parts per million moisture content of the oil at the inlet and outlet bypass valves of the DryKeep® unit. When the inlet and outlet ppm readings converge, the cylinders are saturated. Without the optional instrument package, the customer can use a test instrument, such as the Doble or Vaisala portable unit, to measure the ppm of moisture in oil at both the inlet and outlet bypass valves. Alternatively, take an oil sample at the inlet and outlet bypass valves of the DryKeep® and use the Karl Fischer titration test to determine the ppm moisture content. Always record the top oil temperature when taking samples for the titration test. Again, when the inlet and outlet ppm readings converge, the cylinders are saturated.

Cylinder replacement instructions can also be found here.

What do we do when the cylinder(s) become saturated?

When the cylinder(s) are saturated, they are simply removed while the transformer remains under load and returned for regeneration. Please refer to Appendix C of this Descriptive Brochure for more details.

Cylinder replacement instructions can also be found here.

How often do we need to take oil samples/check the moisture of the oil?

The frequency of oil sampling is recommended as follows:

The first sample should be taken prior to commissioning;

Thereafter, sampling should be taken after 1, 3, and 6 months have passed;

Thereafter, sampling should be done as dictated by normal company maintenance standards and policies.

How can we prove that drykeep® is a cost-worthy investment when compared to a transformer without DryKeep®?

Think of DryKeep® as an insurance policy for your transformer.  Large utilities like ESKOM (South Africa) have repeatedly installed DryKeep® on both new and older wet transformers. Experience has shown that by keeping the moisture in paper at a low level, the life of the insulation increased ten-fold. The relatively low cost of DryKeep® compared to the cost of replacing an expensive transformer more than justifies the relatively small investment.  A small cost for prevention up front can save from having a big cost for a later, major cure.

Can you estimate the increased life time of a transformer (new and old)equipped with DryKeep®?

Each transformer will have a different life span based on the frequency and intensity of the maintenance, ambient temperatures, loading factor, and operating temperatures. We do know that tests performed by Rotek Engineering of South Africa showed that the life of the paper insulation is increased ten-fold when a transformer is equipped with DryKeep®.

The maintenance instructions of DryKeep® don’t specify how frequently the maintenance procedure/inspection should be done such as once a year or twice a year...Etc.?

We cannot dictate how frequently the customer performs their routine maintenance.

Please advise of the characteristics of the molecular sieve

Below is a general description of the product. We cannot divulge the actual size or coatings used in the manufacturing process. This is proprietary information.  

Molecular sieve beads combine the highly selective adsorption properties of Zeolites with high mechanical integrity due to advanced manufacturing and de-dusting technologies. After synthesis, each zeolite crystal is only a few microns across. To be of use in our fixed bed adsorption processes, it is necessary to form particles in a specific diameter. Expertise in molecular sieve beading has led to optimized bead properties for the DryKeep® system. For regenerative applications like petrochemicals drying with zeolite adsorbents, special binders are applied; this gives our molecular sieves a high stability against contaminants in the feed stream, thus allowing a long unit lifetime.

Is the DryKeep® system installed by the customer or by the supplier?

Installation is so simple that typically the customer easily does it themselves.  Power companies prefer not to have strangers working inside their energized substations. They usually have their own workers do the installation. We provide detailed instructions with each DryKeep® unit and are always available for site supervision during installation, or if necessary DryKeep® USA can arrange for a contractor to do

Installation instructions can also be downloaded here.

Is it necessary to shut down transformer when installing DryKeep®?

It is advisable to de-energize the transformer for safety reasons, especially when installing the return piping to the fill valve which is at top area of the transformer. It is not necessary to de-energize the transformer when replacing the saturated cylinders.

How do I know when to replace the particle oil filter?

Most of our customers replace the particle filter when replacing the saturated cylinders or sooner if the transformer is very old and has dirty oil. Some customers change it during their routine inspections which occur mostly every 2 to 3 months.

How would you know when the transformer has been dried down to the safe level?

Before installing DryKeep® on the transformer(s), we will estimate the amount of moisture in the paper insulation. We will request information regarding the transformer characteristics that enables us to determine the moisture content. This allows us to determine how many changes of saturated cylinders will be required before reaching a predetermined safe level of about 1.3% moisture by weight that should be left in the paper. The transformers are dried down to a safe level to avoid re-clamping of the core and coil assembly as it is not always possible to do in the field. To further ensure that over-drying cannot occur, DryKeep® can be supplied with an optional moisture measurement instrument package and, by using a simple PLC, you can program it to shut down the DryKeep® pump when the moisture reaches a predetermined level and have it restart after the moisture builds up again. Refer to Section 7 of the Descriptive Brochure for additional information.

Do transformers need any additional maintenance if equipped with DryKeep®?

No, the transformer is not adversely affected in any way when DryKeep® is installed. It is like any other transformer accessory such as a temperature or pressure gauge installed on a transformer.

What are the applicable standards for the DryKeep® product?

IEEE Standard C57-140-2006, 7.2 written by the IEEE Transformer Maintenance Sub-committee. DryKeep® complies 100% with all the provisions. It is manufactured under ISO 9001 quality standards.

What effect does DryKeep® have on dissolved gases and will it distort our dissolved gas analysis in any way?

To ensure the integrity of dissolved gas analysis, the molecular sieve beads in the DryKeep® cylinders are carefully selected for their preferential bonding with water molecules while excluding bonding with gas molecules. During the development of the DryKeep® system, Eskom Research Institution (TSI) carried out an investigation on transformers ranging in size from 40 MVA to 500 MVA to determine if DryKeep® had any appreciable effect on the interpretation of the DGA. Their conclusion stated that for a continuously gassing transformer, the action of the DryKeep® can never mask the generation of gas and will not significantly affect a trending analysis of gas production rates.

If you have any further questions about the DryKeep® unit, please feel free to contact us.